High efficiency transformation by electroporation of Yarrowia lipolytica.

Yarrowia lipolytica was usually transformed by heat shock, but linearized integrative vectors always resulted in a low transformation efficiency when electroporation was used. To develop a high efficiency integrative transformation method by electroporation of F. lipolytica, we report here that pretreatment of F. lipolytica with 150 mM LiAc for 1 h before electroporation will approximately 30-fold of increase transformation efficiency. A cell concentration of 10(10)/ml and instrument settings of 1.5 kV will generate the highest transformation efficiencies. We have developed a procedure to transform F. lipolytica that will be able to yield an efficiency of 2.1 × 10(4) transformants/ug for integrative linear DNA. With our modifications, the electroporation procedures became a very efficient and reliable tool for F. lipolytica transformation.

Role of the C-terminal domain of Thermus thermophilus trehalose synthase in the thermophilicity, thermostability, and efficient production of trehalose.

Trehalose synthase (TS) from Thermus thermophilus (TtTS) is a thermostable enzyme that catalyzes the conversion of maltose into trehalose by intramolecular transglucosylation. It has a relatively higher thermophilicity and thermostability and a better conversion ratio for trehalose production than other known TSs from different sources at present. By amino acid sequences and the schematic motif alignment of trehalose synthase-related enzymes, it was found that TtTS (965 amino acid residues) contains a particular C-terminal fragment that is not found in most other TSs. To verify the function of this fragment, C-terminal deletion and enzyme fusion were respectively performed to explain the important role this fragment plays in the formation of trehalose. First, the C terminus (TtTSDeltaN, 415 amino acid residues) of TtTS is deleted to construct a TtTSDeltaC containing 550 amino acids. Furthermore, a novel cold-active TS was cloned and purified from Deinococcus radiodurans (DrTS, 552 amino acid residues) and then a fusion protein was created with TtTSDeltaN at the C terminus of DrTS (DrTS-TtTSDeltaN). It was found that the recombinant TtTStriangle upC enzyme had a lower thermostability and a higher byproduct than TtTS in catalyzing the conversion of maltose into trehalose. On the other hand, the recombinant DrTS-TtTSDeltaN enzyme had a higher thermostability and a lower byproduct than DrTS in their reactions. The above-mentioned results allowed the inference that the C terminus of TtTS plays a key role in maintaining its thermostability and hence in modulating the side reaction to reduce glucose production at a high temperature. A new, simple, and fast method to improve thermophilicity by fusing this fragment with particular conformation to a thermolabile enzyme is offered.

Construction of a recombinant thermostable beta-amylase-trehalose synthase bifunctional enzyme for facilitating the conversion of starch to trehalose.

A fusion gene that encoded a polypeptide of 1495 amino acids was constructed from the beta-amylase (BA) gene of Clostridium thermosulfurogenes and trehalose synthase (TS) gene of Thermus thermophilus. The fused gene was overexpressed in Escherichia coli, and a recombinant bifunctional fusion protein with BA at the N-terminal (BATS) or C-terminal (TSBA) of TS having both beta-amylase and trehalose synthase activities with an apparent molecular mass of 164 kDa was obtained. BATS or TSBA catalyzes the sequential reaction in which maltose is formed from starch and then is converted into trehalose. The Km values of the BATS and TSBA fusion enzymes for the reaction from starch to trehalose were smaller than those of an equimolar mixture of BA and TS (BA/TS). On the other hand, the kcat value of BATS approximated that of the BA/TS mixture, but that of TSBA exceeded it. TSBA showed much higher sequential catalytic efficiency than the separately expressed BA/TS mixture. The catalytic efficiency of TSBA or BATS was 3.4 or 2.4 times higher, respectively, than that of a mixture of individual enzymes, showing the kinetic advantage of the fusion enzyme. The thermal stability readings of the recombinant fusion enzymes BATS and TSBA were better than that of the mixture of individual recombinant enzymes. These results apparently demonstrate that fusion enzymes catalyzing sequential reactions have kinetic advantages over a mixture of both enzymes.